JRsbugs, I'm sure there is only on plant. I know the leaves look different, but I did make those pictures to show how different the leaves can be, depending on how 'old' they are. I'm 100% sure it's not Tanacetum vulgare orT. parthenium. I have both plants in my garden and they are really different.
Bonitin, I'm almost sure the plant is no cultivar. I got it from someone who only grows 'natural herbs'. She is German and she only knows the common German names. She told me it's 'Schwarze Edelraute' and after googling it, that resulted in Artemisia genipi, but when I googled Artemisia genipi, I got also pictures of other plants
And like you noticed too: different sites give different plants